The present invention concerns emissive lamps similar to fluorescent lamps comprising emissive material of confined metal oligo atomic clusters in molecular sieves, for instance zeolites.
In recent years, expertise has been gained in the synthesis of zeolites with desired properties by the choice of the structure directing agent (SDA), control of the synthesis conditions, and post-synthesis treatments. (Ref van Bekkum, H., Flanigen, E. M., Jacobs, P. A., Jansen. J. C. (editors) Introduction to Zeolite Science and Practice, 2nd edition. Studies in Surface Science and Catalysis, 2001, 137; Corina, A., Chem. Rev., 1997, 97, 2373-2419; Davis, M. E., Nature, 2002, 417, 813-821; Davis, M. E., et al., Chem. Mater., 1992, 4, 756-768; de Moor P-P. E. A. et al., Chem. Eur. J., 1999, 5(7J, 2083-2088; Galo, J. de A. A., et al., Chew. Rev. 2002, 102, 4093-4138.) At the same time, the family of ordered mesoporous materials has been greatly expanded by the use of different surfactants and synthesis conditions. (Ref: Corina, A., Chem. Rev., 1997, 97, 2373-2419; Davis, M. E. Nature, 2002, 417, 813-821; Galo, J. de A. A., et al., Chem. Rev., 2002, 102, 4093-4138; Ying, J. Y., et al., Angew. Chem. Int. Ed., 1999, 3S, 56-77.) The use of the appropriate template enables the control of the pore size, distribution and connectivity during the zeolite synthesis. For example, use of surfactants such as cetyltrimethylammonium bromide or dodecyltrimethylammonium bromide generally results in formation of mesoporous materials. In a preferred embodiment, the molecular sieves are one or more selected from the group consisting of mordenite, ZSM-5, A-zeolite, L-zeolite, faujasite, ferrierite, chabazite type of zeolites, and mixtures of the foregoing zeolites.
The materials of present invention, for instance zeolites containing oligo silver atom clusters, are cheap and non toxic. Zeolites are currently used in large quantities in washing powder and silver despite its antimicrobial properties, has no known toxic effect on human tissue. Colloidal silver is for instance widely been marketed as a dietary supplement for protective activity against oxidative stress and reactive oxygen species formation.
In contrast to bulk metals which are devoid of a band gap, and hence are good electric conductors, small Au or Ag clusters display interesting emissive properties from discrete energy levels. This phenomenon has been demonstrated e.g., for silver smaller than 100 atoms in rare gas matrices, in aqueous solutions and on silver oxide films. Quantum chemical calculations confirm the molecular character and discrete energy states of these small silver clusters. (Ref 1. Johnston, R. L. (2002) Atomic and Molecular Clusters(Taylor & Francis, London and New York); Rabin, I., Schulze, W., Ertl, G., Felix, C., Sieber, C., Harbich, W., & Buttet, J. (2000)Chemical Physics Letters 320, 59-64: Peyser, L. A., Vinson, A. E., Bartko, A. P., & Dickson. R. M. (2001) Science 291, 103-106: Lee, T.-H., Gonzalez, J. I., & Dickson, R. M. (2002) Proc. Natl. Acad. Sci. USA 99, 10272-10275; Lee, T. H., Gonzalez, J. I., Zheng, J., & Dickson, R. M. (2005) Accounts of Chemical Research 38, 534-541; Bonacic-Koutecky, V, Mitric, R., Burgel, C., Noack, H., Hartmann, M., & Pittner, J. (2005) European Physical Journal D 34, 113-118; Lee, T.-H, Hladik, C. R., & Dickson, R. M. (2003) Nano Letters 3, 1561-1564; Rabin, I., Schulze, W. & Ertl, G. (1999) Chemical Physics Letters 312, 394-398; Felix, C., Sieber, C., Harbich, W., Buttet, J., Rabin, I., Schulze, W., & Ertl, G.
(1999) Chemical Physics Letters 313, 105-109: Rabin, I., Schulze, W., & Ertl, G. (1998) Crystal Research and Technology 33, 1075-1084; Rabin, I., Schulze, W., & Ertl, G. (1998) Journal of Chemical Physics 108, 5137-5142; Konig, L., Rabin, I., Schulze, W., & Ertl. G. (1996) Science 274, 1353-1355; Zheng. J. & Dickson, R. M. (2002) Journal of the American Chemical Society 124, 13982-13983; Bonacic'-Koutecky, V., Veyret, V., & Mitric', R. (2001) Journal of Chemical Physics 115, 10450-10460; Bonacic-Koutecky, V., Pittner, J., Boiron, M., & Fantucci, P. (1999) Journal of Chemical Physics 110, 3876; Bonacic'-Koutecky, V., Cespiva, L., Fantucci, P., & Koutecky, J. (1993) Journal of Chemical Physics 98, 7981-7994; Yoon, J., Kim, K. S., & Baeck, K. K. (2000) Journal of Chemical Physics 1.12, 9335-9342; Fedrigo, S., Harbich, W., & Buttet, J. (1993) Journal of Chemical Physics 99, 5712-5717.)
The major problem in the study and creation of small Au or Ag clusters is aggregation to large nanoparticles and eventually to bulk metal, with loss of emission. Here, it is demonstrated that the use of porous structures with limited pore, cavity and tunnel sizes, overcomes the aggregation problem enabling emissive entities, which are stable in time.
Silver cluster in molecular sieves exhibit remarkable stability. (Ref Bogdanchikova, N. E., Petranovskii, V. P., Machorro, R., Sugi, Y., Soto, V. M., & Fuentes, S. (1999) Applied Surface Science 150, 58-64.) Bogdanchikova et al. found that the stability of the silver clusters depends on the acid strength, which may be related to the composition, e.g. the SiO2/Al2O3 molar ratio, of the molecular sieves. Silver clusters in mordenites having weak acidic sites are stable for at least 50 months, a sufficiently long period with respect to the application in mind for use in a visible light source. Disappearance of the clusters was linked to oxidation. Reduction of the clusters or an oxygen-free or -poor device obviously could increase the stability even more. In one embodiment in the present invention, Au or Ag clusters are protected from oxidation due to encapsulation in the molecular sieves. Additionally, if required, an external coating of the material crystals or capping of the pore entrances can be used to further protect the occluded metal clusters.
The current state of the art has never suggested or demonstrated the room temperature conversion of invisible light, e.g., with energy in the UV region, to a lower energy, e.g., visible light, by oligo atomic metal clusters embedded in molecular sieves.
Some technologies of the art concern the photophysical properties of zeolites loaded with silver. For instance, Chen et al. loaded Y zeolites with AgI, instead of silver clusters, and pumped or charged with 254 nm light, however, without observation or description of visible emission. (Chen, W., Joly, A. G., & Roark, J. (2002) Physical Review B 65, 245404 Artn 245404, U.S. Pat. No. 7,067,072 and U.S. Pat. No. 7,126,136). Calzaferri et al. demonstrated absorption of 254 nm light by silver metal containing zeolites without any notification of emission (Calzaferri, G., Leiggener, C., Glaus, S., Schurch, D., & Kuge, K. (2003) Chemical Society Reviews 32, 29-37.). Kanan et al., showed some emission intensity for silver(I)-exchanged zeolite Y, however only when excited at temperatures below 200 K. (Kanan, M. C., Kanan, S. M., & Patterson, H. H. (2003) Research on Chemical Intermediates 29, 691-704). In summary; the examples do not meet the requirement for applications in lamp or illuminating systems or devices, such as the ones in mind for the present invention.
Present invention concerns the field of visible light lamps, and related, comprising e.g., white light and colored luminescent materials with emission of visible white or colored light at or above room temperature. Such devices thus comprise luminescent materials for photoluminescence based lighting generated through the action of confined metal oligo atomic clusters, more particularly oligo atomic silver clusters loaded in molecular sieves (e.g., zeolites like the A3, A4 and A5 zeolite).
It was particularly found that such emissive materials have properties that are capable of converting light in the UV radiation range such as, but not limited to 254 nm, which is the emission line of the primary Hg UV source commonly used now in fluorescent lamps, to visible light. An additional advantage is the tunability of the devices over the whole UV excitation range. Furthermore, the emissive materials of present invention do not show large absorptions in the visible range, which would lower the overall emission efficiency of the system.
The present invention relates generally to white and colored light emission using confined oligo atomic metal clusters, and more particularly to the use of molecular sieves comprising of these oligo atomic metal clusters as luminescent materials for photoluminescence based lighting.
The extremely high and stable luminescence after activation allows the recording of emission wavelength depending decay curves, demonstrating the existence of multiple emitters. The molecular sieves comprising oligo atomic silver clusters are used as luminescent materials for photoluminescence based lighting.
The bright and stable luminescence of the molecular sieves comprising of these oligo atomic metal clusters in luminescent materials of present invention can be used as a secondary light source in fluorescence lamps or as labels or e.g. bio-labels or security labels.